RIYADH, Saudi Arabia — Defense Secretary Robert M. Gates arrived in Saudi Arabia on Wednesday for a meeting with King Abdullah, opening his third trip to the tumultuous region in the past month.

Gates planned to report to Abdullah on the progress of a $60 billion arms deal with the Saudis and discuss plans for upgrading the nation’s missile defense system, U.S. officials said. Saudi Arabia is the largest buyer of U.S. arms. Iran, which officials say is seeking to exploit the political upheaval in the Arab world, was on the agenda for the visit as well.

Some U.S. officials have bristled at the aggressive role of the Saudi military in last month’s crackdown in neighboring Bahrain. But a senior defense official, speaking on the condition of anonymity, said Wednesday that the relationship between the United States and Saudi Arabia remained strong.

The Saudis sent troops into Bahrain to bolster its monarchy shortly before Bahrain forcefully cleared pro-democracy demonstrators from a central square in the capital of Manama. Bahrain is home to the U.S. Navy’s Fifth Fleet and is regarded as a strategically important bulwark against Iranian power in the region.